cool idle.....

[JimMorrissey]

I tend to idle my machine for less than 30 seconds before shutting it down. Is there any particular reason to idle a diesel that may have been running at 2000-2300 rpm for a couple of hours? It's not a turbo, so I don't see the need to "cool idle" a normally aspirated machine.

 

[thcri]

Turbo or Not, I would still idle any diesel down for a bit. I can't hurt.

murph

 

[Highbeam]

I give it several minutes of cool down idling. Used to be that heads would crack because some of the hot parts would shrink at a different rate than the warm parts. For example, the head is really hot from exhaust and the combustion of hard work but the block is a big piece of iron cooled by mass, surface area, the oil sump and the coolant that goes through the block before getting really hot at the head. That is what I am thinking as I let it idle. I usually use the time for required other things anyway so no time is really wasted.

So the idling at cool down is to allow the various parts of the engine to become the same temperture before being shut off.

 

[Birdman]

I idle down all my equipment before I shut it down. Gas or diesel, it just makes sense to me. While it is ideling I use that time to remove leaves, twigs, mud etc... or check for anything that may need further attention.

 

[JimMorrissey]

I can find nothing to support the concept of "cool idle" for normally asperated diesels on the Web, nor is there any mention of it in my manual. Cool down periods are noted for turbo-diesels only. Obviously it's your machine and it "can't hurt" as mentioned. I was just looking for a factual or scientific reason to do it, as opposed to that's what my grandpa always did, or that's what my brother told me to do. I've never heard of a moden diesel cracking a head from being shut down without idling. That's the beauty of liquid-cooling. Most modern tractors don't run high or hot enough to warrant idling IMO unless one is looking to avoid cooking his turbo bearings.

 

[normde2001]

"Is there any particular reason to idle a diesel that may have been running at 2000-2300 rpm for a couple of hours?

That's always been a confusion factor for me. My tractor runs at the same temp whether it's idling or operating at 2200rpm. Any/all cars I have ever had always run a little hotter when idling, I guess, due to slower waterpump/fan/air speed. Does the combustion chamber actually cool down at idle without showing up in the coolant?

 

[PineRidge]

We have always made a point of running at idle for a few minutes before shut-down and also at start-up.

 

[pennwalk]

The manual for my Yanmar 186D says <font color="blue"> IMPORTANT Stopping a hot engine suddenly could cause damage to certain engine parts by over heating. </font> The manual suggests allowing the engine to idle for one to two minutes to stabilize engine temperature. It is been my habit to let it idle for 5 min after I have worked it but I can't remember where I got that idea. Also I had heard that it was a good idea to let it warm up before working it but that is harder for me. Not enough patience. I compromise by letting it warm up as i drive out to where I am working. /forums/images/graemlins/smile.gif

Chris

 

[cp1969]

Lots of people don't idle their engines before shut down. UPS comes to mind; if anyone would know the adverse effects, if any, from not idling, they would.

The only time I will idle an engine prior to shut down is if it has been working HARD immediately (within a minute or two) before I want to shut it off. That applies to gas engines, too. Otherwise, I shut shut it off.

And all this using dino oil, to boot. I like living on the edge, apparently.

 

[Highbeam]

"I've never heard of a moden diesel cracking a head from being shut down without idling. That's the beauty of liquid-cooling."

Even the old diesels were water cooled. I don't know if you'll find a scientific reason here but it can't hurt and the reasons posted are why it might be wise to err on the side of caution. Is a couple of minutes to let the thing rest that inconvenient?

On my bulldozer I would let it idle until it cooled enough to where I would see a slight blue to the exhaust. That 1972 engine never burned lube oil but the combustion process emmited clear exhaust when hot and that light blue when cool.

Sounds like you already have your mind made up. I would at least let it come to an idle and be sure the temp gauge reads in the normal range. That should only waste a brief moment of your time.